I'm trying to clean up a recording made from the radio about ten years ago. I believe it was dubbed to cassette at one point. The energy for the whole file seems to go "down" more than it goes "up". It's almost like the DC Offset Bias is bad, but that doesn't appear to be the case. The result is audio that sounds overdriven or clipped even though it's nowhere near 0dB.

Does anyone know what the description of this problem is? I'm using Cool Edit Pro (1.3) and I'm sure I can fix it in there, but searches in the help file aren't showing anything because I dion't know what it's called...

Yes, the DC offset needs to be fixed, and Cool Edit will do that for you. But since you mentioned it already, I assume you already tried that and that didn't work.

More likely, the overdriven or clipping sound that you hear is inherent in the audio itself. If this came from a casette dub, the clipping could have happened at any number of stages before it became that wav file you're editing.

Okay, so I'm not as crazy as I thought. To complicate the radio > cassette > computer thing, add > mp3 > wav to the mix and who knows what's happened along the way. If you look closely, it's only above a certain dB level that the bias is showing. Everything below a certain sound level is centered just fine. So forcing a bias adjustment messes up the file even more.

I found a fix sort of by accident. I decided to just live with the problem and went onto doing a little bit of vocal compression (these are old interviews), tape hiss reduction and clip restore. Along the way, each process eliminated more and more of the issue. A final normalizing (with bias adjustment) was icing on the cake. It was a lot of experimenting and luck, but I'm happy with how they're turning out.

And to the Trent Reznor fans, there was much rejoice...

Not perfect, but much better and much harder to detect. Thanks for keeping me from barking up the wrong tree trying to ID the problem.